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JEE Main levelSingle correct optionDifficulty 2 of 3o4118

The relative rates of E1 elimination (together with SN1) of tert-butyl halides in ethanol follow the order

A $(CH X_{3}) X_{3} C - F > (CH X_{3}) X_{3} C - Cl > (CH X_{3}) X_{3} C - Br > (CH X_{3}) X_{3} C - I$
B $(CH X_{3}) X_{3} C - Cl > (CH X_{3}) X_{3} C - Br > (CH X_{3}) X_{3} C - I > (CH X_{3}) X_{3} C - F$
C $(CH X_{3}) X_{3} C - I > (CH X_{3}) X_{3} C - Br > (CH X_{3}) X_{3} C - Cl > (CH X_{3}) X_{3} C - F$
D $(CH X_{3}) X_{3} C - Br > (CH X_{3}) X_{3} C - I > (CH X_{3}) X_{3} C - Cl > (CH X_{3}) X_{3} C - F$

Answer: C

Ionisation is rate determining, so the rate follows leaving-group ability, which tracks the weakness of the C-X bond and the stability of

X X^{-}

. The order is

I X^{-} > Br X^{-} > Cl X^{-} > F X^{-}

.

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